Arteries of the heart, and more specifically coronary arteries, may sometimes be occluded or narrowed by atherosclerotic plaques or other lesions. These afflictions are generally referred to as coronary heart disease or a stenosis, and result in inadequate blood flow to distal arteries and tissue. Heart bypass surgery may be a viable surgical procedure for certain patients suffering from coronary heart disease. However, attendant with traditional open surgery, significant patient trauma, discomfort, extensive recuperation times, and life threatening complications may occur due the invasive nature of the surgery and the necessity for stoppage of the heart during such a surgery.
To address these concerns, efforts have been made to perform interventional cardiology procedures using minimally invasive techniques. In certain efforts, percutaneous transcatheter (or transluminal) delivery and implantation of interventional coronary devices are employed to solve the problems presented by traditional open surgery. Typically, a guide catheter is first inserted through an incision into a femoral (transfemoral), or radial (transradial) artery of a patient. Transradial access is increasingly accepted as a method offering lower post-operative bleeding complications and quicker recovery times for patients. However the smaller diameter of the radial artery requires a smaller diameter guide catheter. The smaller diameter guide catheter has less back support than a similarly configured femoral guide catheter. For example, the Seldinger technique may be utilized in either method for percutaneously introducing the guide catheter. In such methods, the guide catheter is advanced through the aorta and inserted into the opening of an ostium of a coronary artery. A guidewire, or other interventional devices, such as a stent or balloon may be introduced through the guide catheter and maneuvered/advanced through the vasculature and the stenosis of the diseased coronary artery. However, when attempting to pass through a difficult stenosis, or when conducting a radial intervention using a small diameter guide catheter, the guide catheter may not have adequate back support, and continued application of force to advance the interventional device though the stenosis may cause the distal end of the guide catheter to dislodge from the opening of the ostium of the coronary artery, resulting in potential damage to the surrounding tissue.
In order to prevent the guide catheter from dislodging, interventional cardiologists sometimes would deep seat the guide catheter into the coronary artery. The term “deep seat or “deep seating” means that guide catheter would be pushed farther downstream into the coronary artery. However, deep seating the guide catheter risks the guide catheter damaging the coronary artery wall (dissection or rupture), occluding the coronary artery, and interfering with blood flow to the coronary artery.
One attempt to provide additional back support to a guide catheter that has gained acceptance is the use of a guide extension catheter. The guide extension catheter is deployed within a lumen of the guide catheter and extends distally from the distal end of the guide catheter into the coronary artery. Their smaller size (compared to the guide catheter) allows the guide extension catheter to be seated more deeply in the coronary artery with less potential damage. This provides additional back support to the guide catheter to aid in delivery of interventional devices. In cases with a difficult stenosis or radial interventions, the use of the guide extension catheter reduces the risk of dislodging the guide catheter from the opening of the ostium of the coronary artery during treatment.
Because conventional guide extension catheters are used to provide support for guide catheters, such guide extension catheters must be structurally sound. Thus, distal portions of such guide extension catheters conventionally include a wire support or braid, as described in more detail below, to provide strength to the guide extension catheter. It is not desirable to weaken such guide extension catheters. Conventional guide extension catheters are also designed to be smooth such that they can be advanced through tortuous and calcified arteries. Thus, it is not desirable to increase friction of conventional guide extension catheters. Contrast solution is sometimes injected through the guide catheter and guide extension catheter into the coronary artery. It is not desirable for such contrast solution to be lost into the aorta instead of injected into the coronary artery.
Further, even with its smaller size, when deep-seated, the guide extension catheter may occlude the coronary artery. This will interfere with blood flow through the coronary artery and dampen the AO pressure wave measured proximally down the guide catheter.
In particular, during a procedure, the guide catheter fills with blood. A pressure sensor is disposed outside the body and measures blood pressure at the distal end of the guide catheter through the fluid column which fills the guide catheter. Thus, changes in blood pressure at the distal end of the guide catheter propagate through the guide catheter and are measured by the pressure sensor at the proximal end of the guide catheter. However, using a guide extension catheter deep seated in the coronary artery may interfere with blood flow at the coronary artery. Such interference affects the blood pressure measurement at the proximal end of the guide catheter. Specifically, the blood pressure wave is dampened. As explained in more detail below, the measured systolic pressure and measured diastolic pressure both decrease. Further, both decrease such that the normal blood pressure wave flattens or dampens such that it is less like a wave and more like a flat line. This dampened blood pressure wave indicates that blood flow at the distal end of the guide extension catheter has been disrupted. This dampened blood pressure wave also indicates that blood flow to arteries distal of the guide extension catheter has been disrupted, (i.e. reduced) which endangers the patient.
Due to the risks described above, use of a guide extension catheter may result in a sense of urgency on the part of the interventional cardiologist to complete the procedure quickly, which can result in additional complications.
In order to avoid some of these complications, instructions for use of conventional guide extension catheters instruct that the guide extension catheter is to be inserted into vessels significantly larger than the guide extension catheter. For example, instructions for use for a conventional 6 French guide extension catheter (outer diameter of approximately 1.75 mm) states that the product is not to be inserted into arteries with a diameter of less than 2.5 mm.
However, in use and despite the instructions for use, the complications described above persist. Accordingly, there exists a need for an improved guide extension catheter design that provides the needed additional back support to the guide catheter and reduces dampening of the AO pressure wave within the guide catheter, while minimizing the potential to occlude the coronary artery.